1. Field of the Invention
This invention relates to the field of double door locking and more particularly to flush bolt assemblies for locking the inactive door of the double door in place.
2. Description of the Related Art
A flush bolt is used to lock the inactive door of a double door in place. In general, the flush bolt has a bolt that is extended from a top edge, bottom edge or both edges of the inactive door into a hole or receptacle within the doorframe or door sill, thereby locking the inactive door in position. Double doors have become popular for entryways into homes and businesses whereas both doors are opened when large objects must pass through, e.g., when moving furniture, and the inactive door locked in place and the active door used to allow entry of people. However, due to their surface area, double doors have a greater risk of failure due to high winds. During high winds, the double doors tend to flex inwardly and outwardly causing failure along the separation between the doors which is only supported by a door latch and perhaps a deadbolt lock. Furthermore, if the inactive door is inadequately bolted in place, undesired access is possible by an intruder placing inward force at the center of the doors.
Without at least one flush bolt, the structure and security of the double door would be compromised, in that a small force on the doors would override the door latch and/or deadbolt, providing little resistance to wind or burglary. Flush bolts have long been used to lock the inactive door in place, but prior designs have their limitations. Many flush bolts provide a first sliding bolt to lock the inactive door that extends upwardly into the doorframe header and a second sliding bolt extending downwardly into the doorframe sill.
Problems with existing flush bolts occur when the bolts are not locked in place or where the bolts do not extend sufficiently into the doorframe. If the flush bolts do not lock in place, a burglar may easily defeat the bolt by pushing it out of the door frame, thereby allowing the double doors to open by providing a small force inwardly, defeating the door latch and/or deadbolt lock. If the distance in which the bolt penetrates the doorframe is insufficient, the double door may fail during wind or when pushed inwardly. It has been shown that at least two inches of penetration is necessary to prevent the doors from opening during hurricane force winds and several locations in hurricane-prone areas have implemented building codes requiring at least two inches of penetration. Furthermore, as the travel of the bolt increases, friction from the hole or receptacle within the doorframe and/or the door sill makes it increasingly more difficult to engage or release the bolt.
An example of a flush bolt is described in U.S. Pat. No. 6,453,616 to Wright overcomes some of these limitations by screwing the bolt in its extended or retracted position, thereby providing some resistance to burglary. Unfortunately, this requires tools to remove the screws and retaining the screws for later relocking, not something that is readily available in many businesses and homes. Another example is described in U.S. Pat. No. 5,857,291 to Headrick that provides a bolt attached to a handle for moving the bolt between an extended position and a retracted position. This flush bolt provides little resistance to burglary since a thin object can easily be wedged between the inactive and active doors to move the bolt into its retracted position. Another example described in U.S. Pat. No. 6,457,751 to Hartman describes a locking flush bolt using a spring and notch. This provides minimum security and almost no leverage in engaging or disengaging the flush bolt.
What is needed is a flush bolt that will provide a bolt that will pierce the doorframe/sill sufficiently as to provide increased resistance to wind damage while providing leverage to assist in piercing the doorframe and a locking mechanism to prevent unwanted deactivation.